1. Field of the Invention
This invention relates to a fuel hose used for a fuel piping in a motor vehicle or the like. The fuel hose of this invention has a high resistance to gasoline, particularly alcohol-containing gasoline, sour gasoline and amine detergent. It is also suitably used for alcohol and hydrogen which are fuels for fuel cells.
2. Description of the Related Art
The necessity for reducing the amount of gasoline discharged into the atmosphere has recently been pointed out in connection with the environmental problems. Accordingly, the permeation of gasoline through the walls of fuel hoses in motor vehicles has come to be regulated still more strictly. Conventional fuel hoses having a single-layered wall of NBR/PVC (a mixture of acrylonitrile-butadiene rubber and polyvinyl chloride) or the like are not satisfactory for such regulations against the permeation of gasoline.
Alcohol-containing gasoline, which is used for cleaning the exhaust gas of a motor vehicle, is more likely to permeate through the wall of a fuel hose than gasoline not containing alcohol. This is another reason for a demand for a fuel hose having a wall which is less permeable to gasoline.
Therefore, it has been proposed that a fuel hose have a multilayered structure, and particularly that one layer in the multilayered structure be a fluororesin layer of very low permeability to gasoline. These proposals can be roughly classified into two groups depending on the processes employed. According to one group, an uncured rubber tube is laminated with an extruded fluororesin layer, and joined to it by curing. According to the other group, a fluororesin layer is formed on a cured rubber tube by a powder coating method.
One example of the former is disclosed in Japanese Patent Application Laid-Open No. 118549/1996. It discloses an invention in which an uncured tube of epichlorohydrin rubber containing an organic phosphonium salt is laminated with an extruded fluororesin layer and cured. Another example is disclosed in Japanese Patent Application Laid-Open No. 169085/1996. It discloses an invention in which an uncured outer rubber tube and an uncured inner rubber tube are laminated with a fluororesin layer extruded therebetween, and cured. The outer rubber tube is formed from uncured epichlorohydrin rubber containing a salt of 1, 8-diazabicyclo[5, 4, 0]undecene-7 (DBU salt) and an organic phosphonium salt. The inner rubber tube is formed from uncured NBR or fluororubber each containing a DBU salt or an organic phosphonium salt.
One example of the latter is disclosed in Japanese Patent Application Laid-Open No. 255004/1994. It discloses an invention of a fuel hose having a fluororesin layer formed on the inner surface of a cured rubber tube by electrostatically coating it with a fluororesin powder, followed by heating and cooling. According to this invention, pre-treatment, such as sodium etching, corona or low temperature plasma treatment, is applied to the inner surface of the rubber tube to ensure the adhesion between it and the fluororesin layer.
According to the former group of prior art as stated above, the rubber tube and the fluororesin layer adhere well to each other by adhesion in cure. The fluororesin layer formed by extrusion is, however, difficult to form with a small thickness of, say, 0.05 to 0.2 mm or less with good quality. Thus, it has been a problem that, as the fluororesin layer does not have a satisfactorily small thickness, the fuel hose loses flexibility, and eventually cracks, or has its wall layers separated from each other as a result of, for example, vehicle vibration. The fluororesin layer formed by extrusion has a substantially equal thickness along the whole length of the rubber tube. It has, therefore, been a problem that the fluororesin layer formed on the inner surface of the rubber tube makes the hose fail to form a tight seal at the hose connecting end. It has been another problem that a large force is required for the insertion of a pipe into a hose connecting end. It has been still another problem that the extruded fluororesin layer is difficult to form in a corrugated shape.
According to the latter group of prior art as stated above, however, it is easy to form the fluororesin layer with a thickness which is as small as, say, 0.05 to 0.2 mm, or even smaller. It is also possible to select that portion of the rubber tube which is to be coated with the fluororesin powder, and the thickness of its coating to be formed. It is, therefore, possible to form the fluororesin layer not reaching the hose connecting end and thereby avoid the problem of its sealing as pointed out above, when it is formed on the inner surface of the rubber tube. Even in the case where the fluororesin layer is so formed as to reach the hose connecting end, it is possible to form it with a smaller thickness adjacent to the hose connecting end and thereby reduce the force required for the insertion of a pipe thereinto. It is also easy to form the fluororesin layer in a corrugated shape.
In view of the foregoing, a fuel hose having a multilayered structure including a fluororesin layer is preferably manufactured by the latter process.
The latter process has, however, problems not pointed out in the above Japanese Patent Application Laid-Open No. 255004/1994, etc. A fluororesin usually employed for powder coating has a considerably high melting temperature. Therefore, the rubber tube is deteriorated by heat when the fluororesin applied by powder coating is melted and caused to adhere to the rubber tube. This problem may be avoided by using a fluororesin having a low melting temperature, such as a vinylidene fluoride homopolymer. A fluororesin having a low melting temperature is, however, so high in rigidity as to deprive the fuel hose of its flexibility, while not adhering to the rubber layer satisfactorily, either. Another problem is that the pre-treatment mentioned above, such as sodium etching, complicates the manufacturing process.
Under these circumstances, the inventors of this invention made an invention disclosed in Japanese Patent Application No. 196839/1998 (Laid-Open No. 82822/1999). It is a fuel hose having a wall comprising a rubber layer or layers and a fluororesin layer formed from a copolymer of vinylidene fluoride (VDF) and chlorotrifluoroethylene (CTFE) and forming the innermost layer of the wall.
The fluororesin layer forming the innermost layer of the wall gives it high resistance and impermeability to alcohol-containing gasoline, sour gasoline, amine detergent, etc. As the fluororesin has a relatively low melting point, it is possible to avoid any deterioration of the rubber tube by heat when the molten fluororesin is caused to adhere to it. According to this prior application, at least the innermost layer of the rubber tube contains at least one of an organic ammonium salt, an organic phosphonium salt and a polyamine additive, so that a good adhesion can be obtained between the rubber tube and the fluororesin layer without relying upon vulcanization adhesion even if the fluororesin layer may be formed by powder coating.
It has, however, been found by further research that the use of a copolymer of VDF and CTFE as the fluororesin may somewhat reduce the gasoline impermeability of the hose. It has also been found that the addition of an organic ammonium or phosphonium salt, or a polyamine additive is effective for obtaining an improved initial adhesion between the rubber and fluororesin layers, but it is not always effective for maintaining an improved adhesion after the hose is filled with fuel.
It is an object of this invention to provide a simple and effective method of obtaining both an improved initial adhesion between the rubber and fluororesin layers of a hose and an improved adhesion after the hose is filled with fuel, without allowing the deterioration of the rubber layer by heat or any lowering in gasoline impermeability of the hose.
According to a first aspect of this invention, there is provided a fuel hose comprising a single-layered or multilayered rubber tube and a fluororesin layer formed wholly or partially on the inner surface of the single-layered rubber tube or the inner surface of the innermost layer of the multilayered rubber tube, wherein the fluororesin layer is of a copolymer of vinylidene fluoride (VDF) and chlorotrifluoroethylene (CTFE) containing a metal salt in an amount not exceeding 0.3% by weight relative to the copolymer.
The fluororesin layer makes the hose highly resistant and impermeable to alcohol-containing gasoline, sour gasoline, amine detergent, etc. As the fluororesin has a relatively low melting point, it is possible to avoid any deterioration of the rubber tube by heat when the molten fluororesin is caused to adhere to it. As the fluororesin is relatively low in hardness, the hose retains its flexibility. Moreover, the metal salt serves to ensure the low permeability of the hose to gasoline owing probably to its promotion of minute crystallization of the fluororesin copolymer.
According to a second aspect of this invention, the fuel hose satisfies at least one of the following:
(1) the metal salt is a salt of a monovalent or divalent metal;
(2) the metal salt is an inorganic salt of a monovalent or divalent metal such as a halide, a hydroxide, a carbonate and a sulfate thereof;
(3) the metal salt is potassium chloride; and
(4) the content of the metal salt is in the range of 0.05 to 0.3% by weight.
The metal salt is preferably (1), more preferably (2) and still more preferably (3). It is preferably a neutral salt. The content of the salt is preferably selected from the range (4).
According to a third aspect of this invention, the fluororesin layer of the first or second aspect of the invention has a thickness of 0.05 to 0.2 mm. Its thickness as defined ensures the satisfactory flexibility of the hose, while retaining its low fuel permeability.
According to a fourth aspect of this invention, there is provided a fuel hose comprising a single-layered or multilayered rubber tube and a fluororesin layer formed wholly or partially on the inner surface of the single-layered rubber tube or the inner surface of the innermost layer of the multilayered rubber tube, wherein the fluororesin layer is a copolymer of VDF and CTFE and the rubber tube is of a rubber mixture containing acrylic rubber in an amount of 5 to 35 phr (parts per hundred parts of rubber) relative to a base material of the rubber tube. The hose has both an improved initial adhesion between the rubber tube and fluororesin layer and an improved adhesion after fuel filling owing to the acrylic rubber, in addition to the advantages of the fluororesin layer as stated above in connection with the hose according to the first aspect of this invention.
According to a fifth aspect of this invention, the fuel hose of the fourth the aspect satisfies the following (5) and/or (6):
(5) the content of acrylic rubber is from 5 to 25 phr relative to the base material of the rubber tube; and
(6) the acrylic rubber is composed of an alkyl or alkoxy acrylate.
The preferred content of acrylic rubber is defined at (5), and the preferred type thereof at (6).
According to a sixth aspect of this invention, the fluororesin layer in the hose according to the fourth or fifth aspect of this invention has a thickness of 0.05 to 0.2 mm. Its thickness as stated ensures the satisfactory flexibility of the hose while retaining its low fuel permeability.
According to a seventh aspect of this invention, there is provided a fuel hose comprising a single-layered or multilayered rubber tube and a fluororesin layer formed wholly or partially on the inner surface of the single-layered rubber tube or the inner surface of the innermost layer of the multilayered rubber tube, wherein the fluororesin layer is of a copolymer of VDF and CTFE containing not more than 0.3% by weight of a metal salt relative to the copolymer and the rubber tube is of a rubber mixture containing 5 to 35 phr of acrylic rubber relative to a base material of the rubber tube. The hose combines the advantages of the fluororesin layer and the metal salt added to it according to the first aspect of this invention and the acrylic rubber according to the fourth aspect thereof.
According to an eighth aspect of this invention, there is provided a fuel hose comprising a single-layered or multilayered rubber tube and a fluororesin layer formed wholly or partially on the inner surface of the single-layered rubber tube or the inner surface of the innermost layer of the multilayered rubber tube, wherein the fluororesin layer is of a copolymer of VDF and CTFE and the rubber tube is of a rubber mixture containing acrylic rubber in an amount of 5 to 35 phr relative to a base material of the rubber tube containing at least one of an organic ammonium salt, an organic phosphonium salt and a polyamine additive. The hose ensures good adhesion between the rubber tube and fluororesin layer owing to the organic ammonium or phosphonium salt, or polyamide additive which the base rubber contains, while combining the advantages of the fluororesin layer according to the first aspect of this invention and the acrylic rubber according to the fourth aspect thereof.
According to a ninth aspect of this invention, there is provided a fuel hose comprising a single-layered or multilayered rubber tube and a fluororesin layer formed wholly or partially on the inner surface of the single-layered rubber tube or the inner surface of the innermost layer of the multilayered rubber tube, wherein the fluororesin layer is of a copolymer of VDF and CTFE containing not more than 0.3% by weight of a metal salt relative to the copolymer and the rubber tube is of a rubber mixture containing 5 to 35 phr of acrylic rubber relative to a base material of the rubber tube containing at least one of an organic ammonium salt, an organic phosphonium salt and a polyamine additive. The hose combines the advantages of the fluororesin layer and the metal salt added to it according to the first aspect of this invention, the advantages of the acrylic rubber according to the fourth aspect thereof and the advantages of the organic ammonium salt, etc. in the base rubber according to the eighth aspect thereof.
According to a tenth aspect of this invention, the fluororesin layer is formed by powder coating, or causing a fluororesin powder to adhere to the inner surface of the innermost layer of the rubber tube. The layer has a desired thickness and is free from any defects such as pores.
According to an eleventh aspect of this invention, the VDF (A) and CTFE (B) in the fluororesin have a molar ratio A/B of 98/2 to 85/15. This range makes it easy to obtain a fluororesin powder having a low melting point and a flexible fluororesin layer having a low gasoline permeability.
According to a twelfth aspect of this invention, the organic ammonium salt is a DBU salt. It is particularly effective for ensuring adhesion between the rubber tube and the fluororesin layer.